electric motor bearings temperature difference 4

[George V]

Bearing ( ball bearing ) temperature in DE side of electric motor is mostly higher than NDE bearing ( ball bearing ) side by about 10 C.
Can this be explained ?

 

[JJPellin]

Not enough information. I assume it is an induction motor. I assume it is 2 pole. I assume it is a totally enclosed fan cooled design. I assume that the ball bearings are grease lubricated. I assume this is a long term concern and not a new issue. I assume it is not a new motor. I assume it has a proper PM schedule and is being greased according to the manufacturer's recommendations using a high quality Polyurea based grease. I assume it is coupled to a driven machine with a flexible coupling. I assume it is properly aligned to the driven machine. I assume it is running below the nameplate full load amp rating.

If all of my assumptions are correct (very unlikely), it may just be a normal result of the motor design. The fan on a TEFC motor will tend to cool the non-drive end bearing more than the drive end.

Johnny Pellin

 

[dvd]

It is probably a different series of bearing and could have a higher rolling friction coefficient. If there is a belt drive, there would be more load on the DE bearing. Plus if it is a fan cooled motor, the fan cools the NDE the most.

Some good info from SKF -

 

[TugboatEng]

The DE bearing is physically larger in most cases so it will generate more heat when spun at the same speed due to higher velocity. The DE bearing is also the thrust bearing in the motor.

 

[Strong]

"The fan on a TEFC motor will tend to cool the non-drive end bearing more than the drive end."
Agree, and I have confirmed this by temperature measurements on many TEFC motors. DE bearing with belt drive can generate more bearing heat than NDE. The DE bearing can run hotter if driving a hot pump or fan with radiant and conductive (shaft) heat transfer.

Walt

 

[George V]

Many thanks to all.
Bearings are DE and NDE same. All PM followed precisely.
I take your suggestion that cooling fan at NDE cools NDE brg more than DE.
indeed it is a 2 pole motor.
Many thanks

 

[BrianE22]

The DE bearing is also the thrust bearing in the motor.

I'd always thought it was the other way around. Since the DE takes on the most radial load, put the thrust load on the NDE.

 

[electricpete]

I'd always thought it was the other way around. Since the DE takes on the most radial load, put the thrust load on the NDE.

I'm ASSUMING we're talking horizontal (op can clarify).

Horizontal motor typically doesn't have any thrust load to speak of if they drive their load through a flexible coupling.

For a fixed/floating bearing arrangement of horizontal rolling bearing motor, the fixed (thrust) bearing is inevitably (*) on the DE and the ODE floats in the housing (possibly with wavey washer). The float bearing accommodates rotor thermal expansion. If you set it up the opposite way, then the rotor would grow toward the driven machine and could affect the distance between shaft ends which in theory could influence the coupling. Also if you had a fan/impeller directly mounted to the shaft, the fan/impeller would move slightly and could contact a stationary housing. Not that a few thousandths of an inch of axial movement from thermal growth would typically be significant with a flexible coupling between machines or for a direct-mounted fan/impeller whose axial clearances to stationary parts are likely 0.010" or much much more, but that seems to be the logic. Btw there are also (less common) cross-locating arrangements of horizontal electric motor bearings which allow enough endplay to accomodate rotor expansion, with axial movement stopped by ODE bearing in one direction and by the DE in the other direction.

EDIT - * If you have a horizontal motor with cylindrical roller bearings on the DE (typical for motors that have a sheave for belt drive) then that motor will likely have the fixed (thrust) bearing on the NDE.

=====================================
(2B)+(2B)' ?

 

[BrianE22]

Nice EPete - I've spent too much time on worm driven gearboxes .